The present invention relates generally to a magnetoresistive (MR) sensor. More specifically, the present invention relates to an MR read sensor and a method of fabricating the sensor that eliminates the removal of film from the passive regions of the sensor and reduces the coupling dependence between thin film layers.
Magnetoresistive (MR) sensors utilize an MR element to read magnetically encoded information from a magnetic medium, such as a disc, by detecting magnetic flux stored on the magnetic medium. An MR sensor must contain both longitudinal bias and transverse bias to maintain the sensor in its optimal operating range so that it can properly detect the magnetic flux. The dual biasing is established through various combinations of exchange or magnetostatic biasing schemes.
The three critical layers of an MR sensor are the MR element, a spacer material and a soft adjacent layer (SAL). The MR element has magnetoresistive properties and low resistivity and generates an output voltage when a sense current flows through the layer. The SAL is a magnetic bias layer with high resistivity. The SAL biases the magnetization of the MR element and establishes transverse biasing. The spacer material has non-magnetic properties and high resistivity and functions as a spacer between the MR element and SAL. The spacer material helps break the exchange coupling between the MR element and the SAL, which allows the magnetic layers to act as two distinct layers, rather than one strongly coupled layer. Hard-biasing material is placed on each end of the MR sensor, to establish longitudinal biasing and form two passive regions of the sensor. The space between the passive regions maintains the transverse biasing and is referred to as the active region of the sensor.
MR elements can "fracture" into multiple magnetic domains when they are exposed to an external magnetic field. To maximize the stability and output of the MR sensor, it is desirable to maintain the MR element in a single domain state. Three methods for maintaining the MR element in a single domain state are magnetostatic coupling, ferromagnetic exchange coupling and antiferromagnetic exchange coupling. Magnetostatic coupling is accomplished by positioning a permanent magnet adjacent to the MR element. Exchange coupling is accomplished by depositing a ferromagnetic or antiferromagnetic layer adjacent to the MR layer so that one of the magnetic lattices of the magnetic layer couples with the magnetic lattice of the MR element layer to preserve the single domain state of the sensor.
In existing MR sensors, alignment tolerances between various thin film layers and MR sensor mask features are critical. The alignment tolerances in many prior art MR sensor designs greatly increases the complexity of processing because critical geometries frequently require additional and/or more difficult processing steps. Additional processing steps increase the variance and contamination of the various thin film layers.
For example, designs using continuous MR element and SAL films in both the active and passive areas of the sensor are sensitive to the underlayer of the film. In the passive region of the sensor, the SAL film functions as the underlayer for hard-biasing Cobalt-based alloy films. Cobalt-based hard-biasing films are inherently sensitive to the underlayer crystal texture and to the cleanness and roughness of the SAL/Cobalt-alloy film interface. Also in the passive region, the Cobalt-alloy film functions as the underlayer for the MR element. The MR element is sensitive to various factors such as the underlayer crystal texture, cleanness and roughness of the Cobalt-alloy film/MR element interface. The dependence of one film to the other makes the process control inherently difficult in fabricating this type of sensor.
In addition, processes involving reactive ion etching or ion milling often require stopping within a very small tolerance, such as 50 Angstroms. These processes leave the surface of the film layer compromised and affect the exchange coupling. The dependence of one film to an adjacent film makes exchange coupling very critical and affects the overall stability of the MR sensor.
One method for simplifying the process of making an MR sensor is by utilizing an abutting magnetoresistive head. The abutted head appears simple with respect to sensor fabrication. Essentially, a thin MR layer extends over the central active region and a hard-magnetic material is formed over the passive regions. The reliability of the sensor, however, is affected by the abutted junctions between the passive and active regions, which introduce complications in the magnetic and electrical properties at these junctions.
Therefore, there is a continuing need for an MR sensor that reduces the coupling dependence of adjacent films and eliminates the process of reactive ion etching or ion milling various layers, thus decreasing the variance and contamination of thin film layers.